Electric circuit breaker



A ril 18, 1944.

L. S. HQBSON ELECTRIC CIRCUIT BREAKER Filed Aug. 20, 1942 &

lnQefitorc Leland S. Hobson,

His Attorney.

Patented Apr. 18, 1944 2,347, 052 ELECTRIC CIRCUIT BREAKER Leland s. Robson, General Electric New York Drexel Hill, Pa., assignor to Company, a corporation of Application August 20, 1942, Serial No. 455,433

2 Claims.

My invention relates to electric circuit breakers, more particularly to circuit breakers of the gas blast type wherein a blast of arc extinguishing gas such as air under pressure is directed substantially transversely across the arc gap formed upon separation of the contacts, and has for its principal object the provision of an improved circuit breaker of the aforesaid type that is more eflicient in its application of the interrupting blast to the arc and that is capable of subjecting a material length of arc to the interrupting blast during an initial comparatively slight separation of the contacts.

In a successful and well-known type of air blast circuit breaker, such as is disclosed in Prince et a1. Patent 2,284,842, the air blast is directed substantially transversely of the arc to drive the are into an insulating arc chute struc ture where it is extinguished. In this design, the are is drawn across a plurality of arc barriers forming exhaust passages in the chute and the gas blast is applied at the opposite side to drive the are against the barriers and into the pas sages. In this form of cross blast breaker a movable blade contact coacts with a fixed contact opposite the insulating arc barrier edges so that the effective length of arc impinging on one or more barrier edges under action of the gas blast depends, in the case of prompt interruption, on the speed of contact separation. However, notwithstanding the advantage of quickly interrupting the are at the first barrier, high contact opening speeds are often undesirable since additional special devices, such as buffers, auxiliary mechanisms and levers may be necessary to handle the excess energy developed at these high opening speeds.

In accordance with my invention, the arc can be eiliciently interrupted by the gas blast at moderate contact opening speeds when the contacts are still but a very short distance apart. To this end, one or both of the coacting arcing surfaces at the contacts are so shaped that the arc can be readily and quickly extended by the blast into impinging engagement with one of the arc barriers notwithstanding the fact that the actual separatin gap between the contacts may be very slight.

My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 is an elevall tional view in section illustrating a cross bla t air circuit breaker embodying my invention in the open circuit position thereof; Fig. 2 is an enlarged view in section of a part of the breaker shown in Fig, 1 in the initial circuit openin stage; Fig. 3 is a View generally similar to Fig. 2 showing a modified form of my invention; and Fig. 4 is a view also generally similar to Fig. 2 showing another modification of my invention.

The cross-blast type air circuit breaker shown by Fig. 1 comprises relatively movable arcing contacts, such as fixed contact structure I of the finger type and a reciprocally guided bladelike contact 2. The fixed contact is electrically connected as indicated to one line terminal of the breaker at 3 and the blade-like movable contact is also indicated as connected to the other line terminal at 4. The blade contact 2 is movable by suitable actuating means (not shown) along a generally rectilinear path to make and break the circuit with respect to the fixed contact I.

For the purpose of extinguishing the are formed between the contacts when a power circuit is opened, an insulating arc chute 5 is arranged with respect to the contacts so that the arc is drawn at the entrance of the chute directly opposite a gas blast supply conduit 6. The

conduit 6 is suitably connected through a blast control valve (not shown) to a source of compressed gas, such as air, comprising for example a storage tank, and compressor equipment (not shown).

The are chute 5 defines a narrow, diverging space into which the arc is driven and extinguished by the blast and is formed by diverging end walls 1 and 8 and comparatively closely spaced parallel side Walls one of which is shown at 5, connected to a bottom wall l0 through which the blast passage extends. The walls of the chute are composed of a mechanically strong insulating material. such as a molded laminated structure. The exhaust end of the chute is closed except for a laterally extending conduit or stack H which directs the heated blast gases away from the circuit breaker proper.

The chute alsoincludes a plurality of insulating arc barriers l2 and I3 that are disposed edgewise to the are path with the barrier width transversely of the arc path so as to form diverging gas passages in which are spaced metal cooling plates l4 leading to the exhaust conduit. The barriers extend fairly close to the arc path as indicated and are composed of a vaporizable insulating material such as hard fibre that does not lose its insulating characteristics in the presence of the arc. A circuit breaker of this character is disclosed and claimed in the above mentioned Prince et al. Patent No. 2,284,842.

The arc chamber or space in which the arc is drawn is formed at the entrance of the chute between the blast supply conduit 6 and the arc barriers I2 and I3 and constitutes an elongated chamber l5 having at one end an opening IS in registry with the movable contact 2 which can move exteriorly of the chute to a safe isolating distance. The barrier I3 extends entirely across the arc chamber for confining the arc flame to the chute interior and has a slot 13" also in registry with the contact 2. The arc formed between the separated contacts may extend longitudinally of the chamber as is evident from Fig. 1 so as to be in the direct path of the gas blast as it is directed into the chute.

The blast supply conduit 6 in the present instance communicates with a passage 6' that bypasses the barrier l3 for the purpose of preventing arc flame in the interrupting chamber from following the movable blade contact when it is withdrawn from the chute. This feature per se constitutes no part of the present invention and is described and claimed in Rankin Patent 2,290,708, granted July 21, 1942, and assigned to the same assignee as the present invention.

In Fig. 2 the circuit breaker is shown partly open, the blade contact 2 having moved but a very short distance away from engagement with the contact I to form an arc gap. The arcing is preferably confined to special arcing portions or tips l and 2' on the fixed and movable contacts respectively. It will, therefore, be noted that the arc gap initially is formed adjacent to and across the entrance to the first exhaust passage defined by the barrier l2 and the arc chute and wall 8. The movable contact, as it is withdrawn from the chute uncovers the other exhaust passages in succession. The are chute end of the blast supply conduit 6 is formed as shown at 6" so as slightly to deflect the blast and direct it in an oblique direction across the path ofcontact movement, i. e. the arc gap. This direction of the blast is indicated by the center line H of the exhaust passage 6". Specifically, the blast is directed obliquely against arcin tips I of the fixed contact structure and also toward the entrance of the exhaust passage l2.

Heretofore, the blade contact 2 has been provided with a rectangular shaped arcing tip arranged so that contact separation at both stationary arcing tips I occurs substantially simultaneously. In such an arrangement it should be noted that the blade contact must move a material distance from the fixed contact before the initially formed arc can be looped by the blast against theedge of the first barrier E2. The are is often interrupted at the first arc barrier. In other words, satisfactory arc interruption often depends on drawing the arc to a predetermined length and the opening speed of the breaker therefore must be sumciently high to form an effective length of arc in order to interrupt the circuit within a half cycle or so.

I have found that the contact opening speed can be moderate without sacrificing arc interrupting speed by designing the contact arcing structure, such as the blade contact, for example, so that a horn-gap effect on the arc is obtained instantly upon separation of the contacts.

interrupting blast is effective to bring about circuit interruption generally at the first current zero. In the specific arrangement shown by Figs. 1 and 2, the blade contact 2 at the down-stream side'of the arcing tip 2' is cut away and tapered away from the blast as shown at 2 for producing the horn-gap efiect above referred to. This can be best explained by reference-to Fig. 2.

Let it be assumed that the blade arcing tip 2' has just-parted contact with the upstream fixed arcing tip I so that a small initial arc gap is formed. The interrupting gas under pressure in the chamber l5 immediately blasts its way through the gap toward the first chute passage I2 and quickly drives the arc to the downstream side of the blade where its root on the blade contact runs along the sloping arcing surface 2" to extend the arc in the form of a loop as illustrated. This extension of the arc is also iacilitated by the magnetic forces of the arc current which tend to expand the loop according to well-known principles. There is now sufiicient arc length in the interrupting space at the first barrier l2 to enable the blast to force the arc against the barrier and to interrupt the circuit at the first current zero even though the contact end of the blade has still a material distance to move before being opposite the barrier.

Since the arc length required for efiicient circuit interruption is much greater than the length of the arc gap required for insulating the contacts from each other after current interruption, it will be appreciated that my invention is a solution to the problem of high speed circuit interruption at moderate contact opening speeds. With my invention, interruption may be possible with actual contact separation of as little as A; inch or so.

In the modification shown by Fig. 3, the downstream fixed arcing contact I' is tapered at l" to form a horn-gap arcing surface so that immediate extension of the arc can proceed upon initial separation of the contacts. In addition, an arc runner 8' mounted on the arc chute wall 8 cooperates with the tapered arcing tip so that the arc root at that terminal can be transferred by the blast from the arcing surface I" to the arc runner. The are, as diagrammatically illustrated, is extended and driven by the blast and magnetic forces directly against the edge of the first barrier l2. Circuit interruption, as in the previous case, can therefore take place at the first current zero with but slight actual separation of the contacts.

The arrangement shown by Fig. 4 is in certain respects similar to that of Figs. 1 and 2 since substantially the same fixed and movable contact structures are used. Accordingly, similar reference numerals indicate similar structure of the circuit breaker. This is provided in addition a fixed auxiliary electrode E in sliding electrical contact with the trailing or downstream edge of the contact blade 2 so that the electrode arcing surface e' defines with the fixed arcing contacts 6' an arc gap that is optimum in respect to the gas blast extinguishing action. That is, it has been found that a power arc can be interrupted to advantage by a gas blast when the arc is held to a gap of predetermined length depending upon the circuit voltage and other factors, and the gap above referred to represents this length.

In accordance with my invention I combine such an arrangement for establishing a preferred arc gap with the contact horn-gap structure previously described so that the arc can be quickly extended to the preferred length in response to comparatively slight opening movement of the contact blade, and then can be held at this gap while being subjected to the interrupting gas blast as the contact blade continues to move toward its isolating position. In practice, the arc is quickly moved from the contact blade to the auxiliary electrode and is interrupted before the blade moves out of conducting engagement with the auxiliary electrode so that the blade then can safetly move to its isolating position exteriorly of the arc chute. With this arrangement the gas blast can act for a materially longer time on the preferred length of arc since very little time is required for the arc to reach the preferred length or optimum when the circuit is initially opened. This insures comparatively high interrupting speed.

It will be apparent that the auxiliary electrode can also be applied to the blade of the arcing structure shown by Fig. 3 in essentially the same manner for obtaining the results above described.

Although I have shown my invention as applied alternatively to arcing structure at the movable and fixed contacts, it should be understood that it may be applied at both contacts as well.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gas blast circuit breaker comprising an insulating arc chute, relatively movable arcing contacts separable in said chute, a separate auxiliary electrode arranged to electrically engage one of said arcing contacts so as to form with said arcing contacts upon separation thereof an optimum fixed arc gap of substantially predetermined length, are extinguishing structure in said chute at one side of said are gap, and means for directing a blast of interrupting gas from the opposite side of said arc gap into said chute to traverse the arc gap, the arcing structure at one of said contacts having a cutaway angular arcing surface at the downstream side thereof, said arcing surface forming in effect with the cooperating arcing surface a horn gap for facilitating rapid extension of the arc to said optimum gap at said auxiliary electrode and into said are extinguishing structure immediately upon separation of said contacts.

2. A gas blast circuit breaker comprising an insulating arc chute having an insulating barrier forming exhaust passages in said chute, a fixed arcing contact and a movable blade arcing contact separable to form an arc gap opposite said barrier and passages, means for directing a blast of interrupting gas from the opposite side of said are gap into said chute to traverse the arc gap, said blade contact having at its arcing end at the downstream side thereof an angularly disposed arcing surface forming with the cooperating fixed arcing surface a diverging horn gap for facilitating immediate extension of the are into impinging engagement with said barrier upon separation of said contacts, and a separate auxiliary electrode arranged to be in electrical contact with said blade positioned at said are gap so as to form a relativelyshort fixed optimum gap with said fixed contact immediately upon extension of said arc.

LELAND S. HOBSON. 

